As we have seen, making even a temporary ohel is rabbinically prohibited. Included in this prohibition is placing a wide board or a sheet across vertical supports to protect oneself from the elements. However, when the supports are not permanent, this can be permitted if the ohel is erected in a manner that differs significantly from the normal way of doing it. The Sages forbade putting up a temporary ohel in the usual order – first putting up the walls or supports, and only then putting up the roof. However, if the order is reversed, the Sages permit one to put up a temporary ohel. Thus, if the roof is first held up in the air and then walls or supports are placed underneath it, this would be permitted. Usually a second person is necessary in order to erect a tent in this way (Shabbat 43b; SA 311:6; Bi’ur Ha-Gra ad loc.).
These rules apply to children’s games as well. Children who are of an age where they can understand the laws of Shabbat may not spread blankets over chairs in order to create a tent in which to play, but they may hold the blanket in the air and then place chairs underneath it. Similarly, they may not use interlocking toy bricks (like Lego) to build a house or garage whose inside area is a square tefaĥ or more, but they may hold the roof up and then attach the walls from underneath.
Just as one may not put up a temporary ohel, one may not take one down. Just as one may put up a temporary ohel if he changes the order of construction, so too he may take one down if he changes the order. The walls must be removed first, and only afterward the roof (SSK 24:22).
Even if there is no intention to erect an ohel in order to take shelter under it, nevertheless, if in actuality one makes something in the form of an ohel and the space underneath serves a purpose, it may not be erected in that form. For example, one may not take two barrels of wine and place a third one across the top. Since it is necessary to have airflow between the barrels so that the wine will not get overheated and spoil, this structure is considered a temporary ohel: the two barrels are considered walls, and the barrel atop them is considered a roof. However, the Sages permit doing so if the order is reversed; one person may hold up the top barrel while someone else slips the other two barrels underneath.
One may place a tabletop on legs as long as each leg is less than a tefaĥ wide. In such a case, the legs are not considered meĥitzot, and one may set the legs first and then place the tabletop on top of them. If each of the legs is a tefaĥ wide, they are considered meĥitzot. If one wishes to set up such a table, he must hold the tabletop in the air and then have someone else slip the legs underneath it. In contrast, when opening a folding crib, one may place the board and mattress normally, as there are no walls beneath them and there is no purpose served by the space underneath them.
One may open a baby carriage or stroller, a folding table, a folding chair, a cot, or a playpen on Shabbat because the entire structure is already completed and connected before Shabbat. The only part that is done on Shabbat is opening it (SA 315:5).
One may not cover a very large barrel (whose diameter is close to a meter), as this resembles making an ohel if a tefaĥ of open space remains (Shabbat 139b; SA 315:13). However, if the cover of the barrel has a handle on it, then it is clear that this is simply the cover of a receptacle and not the roof of a tent, and thus one may place it on top of the barrel (SSK ch. 24 n. 72). One may overturn a large pot and use it to cover food and protect it from the sun or insects, because overturning a pot is not considered making an ohel. Similarly, one may overturn a recliner or couch even though space is created underneath it, because overturning furniture is not considered making an ohel (BHL 315:5, s.v. “kisei”).
Many maintain that it is rabbinically forbidden to put on a hat with a hard brim a tefaĥ wide, because doing so is considered making a temporary ohel. This is despite the fact that one may use a hand fan to shield himself from the sun and hold a talit horizontally over one who is called up to the Torah in honor of his marriage. Nevertheless, a hat that remains on one’s head without moving is more similar to a temporary ohel (Shabbat 138b; Rabbeinu Ĥananel; Rambam; SA 301:40). The custom, though, is to be lenient and to allow one to wear a black hat, since it is worn primarily for the sake of honor and not to provide shade. It is also possible that the brims of today’s hats are not considered hard (MB 301:151). Alternatively, perhaps the custom relies on Rashi, who maintains that a hat is never comparable to an ohel; the only concern is that if one’s hat is blown off, people might chase after it and end up carrying it.
The universal custom is to forbid using an umbrella on Shabbat because it resembles an ohel (see BHL 315:8, s.v. “tefaĥ”; SSK 24:15).